Constant expressions

Constant expressions can be used in all languages for assigning a variable with a value. All constant expressions have a well defined data type according to their semantics. If you program an operation between variables and constant expressions having inconsistent data types, it will lead to syntactic errors when the program is compiled. Below are the syntactic rules for constant expressions according to possible data types:

BOOL: Boolean

There are only two possible boolean constant expressions. They are reserved keywords TRUE and FALSE.

SINT: Small (8 bit) Integer

Small integer constant expressions are valid integer values(between -128 and 127) and must be prefixed with "SINT#'. All integer expressions having no prefix are considered as DINT integers.

USINT / BYTE: Unsigned 8 bit Integer

Unsigned small integer constant expressions are valid integer values(between 0 and 255) and must be prefixed with "USINT#'. All integer expressions having no prefix are considered as DINT integers.

INT: 16 bit integer

16 bit integer constant expressions are valid integer values(between -32768 and 32767) and must be prefixed with "INT#'. All integer expressions having no prefix are considered as DINT integers.

UINT / WORD: Unsigned 16 bit integer

Unsigned 16 bit integer constant expressions are valid integer values(between 0 and 255) and must be prefixed with "UINT#'. All integer expressions having no prefix are considered as DINT integers.

DINT: 32 bit (default) integer

32 bit integer constant expressions must be valid numbers between  -2147483648 to +2147483647. DINT is the default size for integers: such constant expressions do not need any prefix. You can use "2#", "8#" or "16#" prefixes for specifying a number in respectively binary, octal or hexadecimal basis.

UDINT / DWORD: Unsigned 32 bit integer

Unsigned 32 bit integer constant expressions are valid integer values(between 0 and 4294967295) and must be prefixed with "UDINT#'. All integer expressions having no prefix are considered as DINT integers.

LINT: Long (64 bit) integer

Long integer constant expressions are valid integer values and must be prefixed with "LINT#'. All integer expressions having no prefix are considered as DINT integers.

REAL: Single precision floating point value

Real constant expressions must be valid number, and must include a dot ("."). If you need to enter a real expression having an integer value, add ".0" at the end of the number. You can use "F" or "E" separators for specifying the exponent in case of a scientist representation. REAL is the default precision for floating points: such expressions do not need any prefix.

LREAL: Double precision floating point value

Real constant expressions must be valid number, and must include a dot ("."), and must be prefixed with "LREAL#". If you need to enter a real expression having an integer value, add ".0" at the end of the number. You can use "F" or "E" separators for specifying the exponent in case of a scientist representation.

TIME: Time of day

Time constant expressions represent durations that must be less than 24 hours. Expressions must be prefixed by either "TIME#" or "T#". They are expressed as a number of hours followed by "h", a number of minutes followed by "m", a number of seconds followed by "s", and a number of milliseconds followed by "ms". The order of units (hour, minutes, seconds, milliseconds) must be respected. You cannot insert blank characters in the time expression. There must be at least one valid unit letter in the expression.

STRING: Character string

String expressions must be written between single quote marks. The length of the string cannot exceed 255 characters. You can use the following sequences to represent a special or not printable character within a string:

Examples

Below are some examples of valid constant expressions

Below are some examples of typical errors in constant expressions